1. Field of the Invention
The present invention relates to a laser-welding head. More specifically, the present invention relates to a laser-welding head capable of pressing overlapping workpieces close together for welding, such as lap welding for welding together component members of an automotive body.
2. Description of the Related Art
When welding together two overlapping steel sheets by lap welding which presses the two overlapping steel sheets close together and irradiates overlapping parts of the steel sheets with a laser beam, such as lap welding for welding overlapping component members of an automotive body, a welding head capable of pressing together overlapping workpieces and of welding the overlapping workpieces is attached to the extremity of, for example, the robot arm of a laser-welding robot, and the laser-welding robot moves the welding head along a weld line previously taught to the laser-welding robot various laser-welding heads have been proposed.
A laser-welding machine proposed in JP-A No. Hei 3-57580 is provided with a pressing unit including a roller for pressing parts of workpieces near a weld line along which a spot of a laser beam emitted by a laser unit is moved, and a spring for pressing the roller against the workpieces.
A laser-welding robot proposed in JP-U No. Hei 4-80682 includes a movable rolling member, a cylinder actuator holding the rolling member for vertical movement, and a stationary rolling member supported at a fixed position opposite to a head. Overlapped workpieces are held between the movable rolling member and the stationary rolling member for welding.
A laser-welding method proposed in JP-A No. Hei 10-113783 uses a local pressing unit including a pressing cylinder actuator and a steel ball, and welds together workpieces pressing the workpieces by the local pressing unit.
When welding workpieces together by the laser-welding machine proposed in JP-A No. Hei 3-57580, however, the spring is strained according to the vertical undulations of portions of the workpieces along a weld line and the pressure applied to the roller varies accordingly. Consequently, the roller is unable to apply a fixed pressure to the workpieces. Such a problem may be solved by using a constant-force spring. However, a constant-force spring having a large loading capacity on the order of 100 kgf is very large and hence it is difficult to incorporate such a large constant-force spring into the laser-welding machine. Moreover, the pressure to be applied to the workpieces by the constant-force spring is unadjustable.
The laser-welding robot proposed in JP-U No. Hei 4-80682 and the laser-welding method proposed in JP-A No. Hei 10-113783 need a large cylinder actuator and a large space for installing the large cylinder actuator, and need complicated control operations using a control valve for controlling the cylinder actuator having a large stroke capacity for minute actions.
The present invention has been made in view of the foregoing problems in the prior art and it is therefore an object of the present invention to provide a laser-welding head capable of applying a constant pressure to parts of workpieces to be welded together regardless of the undulation of the parts of the workpieces to be depressed and of adjusting the constant pressure to be applied to the parts of the workpieces to a desired level.
According to the present invention, a laser-welding head comprises a pressing device capable of moving along parts of workpieces near a weld line to press together the same parts of the workpieces, a pressing unit for applying a predetermined pressure to the pressing device to press the pressing device toward the parts of the workpieces near the weld line, and a laser beam projecting unit mounted on the pressing unit for movement together with the pressing device, wherein the pressing unit includes a pneumatic cylinder actuator for applying the predetermined pressure to the pressing device.
In the laser-welding head, it is preferable that the pressing unit includes a support member and a movable member capable of moving relative to the support member, the pneumatic cylinder actuator has an air cylinder supported on the support member, and a piston rod having one end fastened to the movable member, the pressing device is supported on the movable member, and the laser beam projecting unit is mounted on the movable member.
Preferably, the pneumatic cylinder actuator is connected to an air-pressure control means, and the air-pressure control means controls the pressure of compressed air supplied to the pneumatic cylinder actuator to apply a desired pressure to the movable member.
Preferably, the movable member is movable relative to the support member along a linear guide formed on the support member.
Preferably, the stroke of the piston rod of the pneumatic cylinder actuator is smaller than the diameter of the pressure-bearing surface of the piston rod.
Preferably, the stroke of the piston rod of the pneumatic cylinder actuator is in the range of 1 to 5 cm.
Preferably, the support member is mounted on the extremity of a robot arm.
Preferably, the position of the laser beam projecting unit on the pressing unit is adjusted by a fine-adjustment device.
Preferably, the fine adjustment device consists of first and second fine-adjustment mechanisms for moving the laser beam projecting unit laterally with respect to the weld line and moving the same vertically.
Preferably, the laser beam projecting unit is held on the pressing unit by the fine adjustment device so as to be movable relative to the position of the pressing device.
Preferably, the pressing device has a roller.
Preferably, the roller is supported with its flat side surface inclined at a predetermined angle to a direction in which a laser beam projected by the laser beam projecting unit travels.
Preferably, the roller is supported such that the flat side surface thereof extends along the profile of the focused laser beam projected by the laser beam projecting unit.
Preferably, the part of the workpiece with which the roller comes into contact is exposed to the laser beam when the laser beam is not focused.
Preferably, the pressing device has a roller support structure fixed to the movable member, and a roller supported for turning on the roller support structure.
Preferably, the roller support structure includes an upper member having an L-shaped cross section, an intermediate member having a substantially L-shaped cross section, having an inclined surface inclined outward with respect to the movable member, and joined to the upper member, and a roller support member joined to the inclined surface of the intermediate member to support the roller with its flat side surface inclined to a vertical.
Preferably, the laser beam projecting unit projects a laser beam emitted by a YAG laser.
Preferably, the pressing unit is mounted on the extremity of a robot arm.
Preferably, parts to be welded together are overlapping parts of first and second workpieces.
According to the present invention a robot is provided with the laser-welding head according to the present invention.
The laser-welding head of the present invention is capable of always applying a fixed pressure to the parts of the workpieces to be welded, of applying a pressure to the workpieces and of varying the pressure, and can be formed in compact construction.